The present invention relates in general to the field of telecommunication, and more specifically to the field of wireless telecommunication.
Conventional public land mobile telephone networks (PLMN)xe2x80x94i.e. cellular radio telephone systemsxe2x80x94include a land system and one or more mobile stations (MS). The land system typically includes at least one mobile switching centre, which is connected to one or more radio base stations (RBS). Normally, one or more of the mobile switching centres are also connected to a public switched telephone network (PSTN), i.e. a normal (non-mobile) telephone system. Each radio base station serves at least one geographical area known as a cell. Mobile stations that are positioned in the cell(s) communicate with the radio base station via a radio interface. The mobile stations communicate, via the radio base stations and the mobile switching centres, with other mobile stations in the PLMN or with telephones connected to the PSTN.
Most PLMN systems used today were originally designed for speech communication. The switching technology used in the PLMN system is therefore typically so called circuit switching, which is also used in the conventional PSTN. This means that there is a dedicated two-way connection set up between two of the mobile stations (or between one of the mobile stations and one fixed telephone in the PSTN) continuously for the whole duration of a call, even if no information (e.g. speech) is in fact transferred. Circuit switching is suitable for applications having need for continuous flows of information, which are delay sensitive but not bit error sensitive, e.g. speech and video communication.
Today, however, there is an increasing interest in data communication, e.g. electronic mail, internet, file transfers and the like. For many forms of data communication circuit switching is, however, not the optimal solution. Packet switching is an alternative form of switching, which is often more suited for data communication. The information, that is to be transferred through a packet data network employing packet switching, is divided into packets, which need not be of equal length. Each data packet contains an address indicating its destination. When the data packet reaches a node of the packet data network, it enters a buffer. Typically, the packet is then checked for bit errors, e.g. by means of cyclic redundancy check (CRC), that might have occurred during transmission, and a retransmission is requested if bit errors are detected. The error checking and the retransmission do, however, cause delays in the transferring of information. If no bit errors are detected, the address of the packet is read and the packet is forwarded to a next node. This is repeated until the packet reaches its destination. At the destination the packets are collected, and the original information is assembled from the packets. In packet switching there is no dedicated connection (channel) for each user. The transfer of information requires only as much (or little) of the channel resources (e.g. bandwidth or time) as is necessary. Packet switching is normally not suited for speech and video communication, due to the delays involved, but is highly suited for most forms of data communications, thanks to the high accuracy that results from error checking and retransmission.
Wireless packet data networks have also been designed. The wireless packet data networks are normally constructed as overlay systems on the existing PLMN, e.g. CDPD (Cellular Digital Packet Data) for AMPS and D-AMPS systems. The land system is then complemented with a Packet Data Backbone Network (PDBN) to which the mobile switching centres of the PLMN are connected. The packet data backbone network comprises one or more Packet Data Intermediate Systems (PDIS) which, among other things, perform the packet switching within the land system. The PDBN is also connected to one or more fixed end systems, e.g. internet, intranets or a computer (e.g. a PC).
The packet data communication between one of the mobile stations and one of the base stations takes place on a radio channel comprising an uplink carrier and a downlink carrier, which have been reserved for packet data communication. The mobile station sends packets of data to the radio base station on the uplink carrier and receives packets of data from the radio base station on the downlink carrier. The mobile station also receives control messages from the radio base station on the downlink carrier, informing the mobile station on when it shall send data packets on the uplink carrier or receive data on the downlink carrier. This means that the same uplink carrier and downlink carrier can be shared by several of the mobile stations for packet data communication.
In order for the radio base stations to handle packet data, they must, however, be modified with new hardware as well as with new software. One known solution is an integrated solution in which a mobile data device (MDD) is installed in the radio base station, and transceivers in the radio base station are provided with new software, allowing them to handle packet data. The MDD is, among other things, arranged for providing control of packet data functions in the transceivers and for enabling packet data communication between the radio base station and the packet data backbone via the mobile switching centre. Another known solution is an overlay solution with an external packet data base station unit, which is connected to the radio base station. The external packet data base station unit is arranged for using the existing antenna functions of the radio base station, although having its own transceiver(s) and its own MDD. The external packet data base station unit is normally connected to a channel serving unit (CSU), which is arranged for inserting and dropping the transferred information into/from time slots on the Pulse Code Modulation (PCM) link connection between the radio base station and the mobile switching centre.
However, with the above solutions, the full deployment of packet data coverage in the public land mobile telephone network becomes costly and requires a lot of engineering work, since each and every one of the radio base stations has to be individually modified with new hardware as well as with new software.
The present invention addresses the problem of obtaining a wireless communication system for speech and packet data communication wherein deployment, control and maintenance of packet data functions becomes simpler and less costly.
The above stated problem is solved in short with a wireless communication system according to the following. The wireless communication system comprises one or more mobile switching centres having group switches. Radio base stations having transceivers programmed with software for handling packet data operation are connected to the mobile switching centre(s). The wireless communication system comprises also a packet data backbone, which is connected to the group switch(es) of the mobile switching centre(s). One or more centralised mobile data devices are connected to the group switch(es) of the mobile switching centre(s). The centralised mobile data device(s) is/are arranged for controlling packet data functions of radio base stations having transceivers with packet data software via the group switch(es) of the mobile switching centre(s).
The object of the invention is thus to obtain a wireless communication system for speech and packet data communication, wherein deployment, control and maintenance of packet data functions becomes simpler and less costly, and the invention comprises such a wireless communication system.
The way in which the present invention solves the above stated problem can be explained in somewhat more detail according to the following. Deployment of packet data functions is done by installing software for packet data communication in the transceivers and, if needed, by adding processing capacity to the central mobile data device(s). There is no need for visiting a radio base station site for deployment of packet data functions, since no hardware reconfiguration of the radio base stations is needed and since software for packet data communication can be installed in the transceivers remotely from the mobile switching centre(s). Deployment of packet data functions thus becomes simpler and less costly. It is also easy to reallocate packet data resources between cells depending on varying demand for packet data communication in the cells, this further adding to flexibility and efficiency in use of system resources, leading in the end to an increase in overall cost efficiency. The control of packet data functions becomes simpler and less costly, since the control of packet data functions of a plurality of radio base stations can be done by one centralised mobile data device, instead of having one mobile data device installed in each of the radio base stations. Maintenance work also becomes simpler and less costly, since there is no need to visit the individual radio base stations in order to perform maintenance work relating to packet data functions.